There has been known a fuel tank assembly in which a fuel pump unit is provided below a fuel tank for the purpose of fully sucking the fuel in the fuel tank (see Patent Document 1, for example). This is an example of using a vertically elongated fuel tank. When the fuel level in the fuel tank assembly having such a vertically elongated fuel tank is detected by a fuel level gauge that uses a float supported on a float arm, detection of the fuel level in as wide a range as possible is required from a highest limit level to a lowest limit level. To cope with such requirement, the float arm is made long to widen the range of fuel level detection by the fuel level gauge.
There has also been known a fuel tank assembly in which the fuel tank is made elongated in the front-to-rear direction of the vehicle and made flat in the vertical direction, for the purpose of increasing the capacity of the fuel tank without elevating the height of the rider's seat (see Patent Document 2, for example). If the structure of the above fuel tank assembly with a vertically elongated fuel tank disclosed in Patent Document 1 were applied to the structure, disclosed in Patent Document 2, having a flat fuel tank elongated in the front-to-rear direction, the fuel level gauge associated with the flat fuel tank having a reduced height would not ensure detecting the fuel level in a sufficiently wide range.